1. Field of the Invention
This invention relates generally to the field of telecommunications. More specifically, the invention relates to an apparatus for maintaining antenna polarization in a cellular telephone handset.
2. Related Art
In existing cellular telephone networks, signals in the 900 MHz frequency band are communicated between a base station and a portable telephone. The base station antenna transmits vertically polarized signals. The portable units use simple pole (i.e., monopole or dipole) antennas.
In order to maximize the signal level received by a portable unit, it is desirable to maintain the antenna of the portable unit in a vertical orientation. Unfortunately, most commercially available portable units have a fixed antenna generally oriented to align with the long axis of the unit. When the portable unit is held in alignment with the mouth and ear of a user, this generally orients the unit at approximately a 45.degree. angle with respect to vertical. This results in a polarization mismatch with the vertically polarized signals being received from the base station. This polarization mismatch results in a loss in received signal power. For example, at a 45.degree. angle from vertical, the received signal will have an amplitude 3 dB [i.e., 20log(cos 45.degree.)] lower than that received by a vertically oriented antenna.
What is needed is a means for assuring a substantially vertical antenna orientation in portable units so that signal attenuation resulting from polarization mismatches can be minimized.